This invention relates to a four-stroke cycle engine unit to be incorporated in a portable working machine, and more particularly, to a lubricating device of a four-stroke cycle engine unit.
A portable working machine such as a lawn mower, a trimmer and a chain-saw is equipped with an internal combustion engine unit. In such a portable working machine, it is required for the engine unit to have a relatively compact structure and light weight because such a working machine is operated by hands of an operator and also required to be revolved with high rotation speed. It would also be better to be manufactured with a cheap cost. Such requirements may be satisfied by incorporating a two-stroke cycle engine in the machine.
In comparison of such a two-stroke cycle engine unit with a four-stroke cycle engine unit, the latter engine unit generates noise lower than that of the former engine unit and generates relatively clean exhaust gas, and the latter engine unit is operated with a reduced fuel consumption. In these points, the latter engine unit may be superior to the former engine unit.
However, the common portable working machine is often used in an inclined or an inverted posture.
The engine unit is lubricated in a way that a mist of a lubricating oil in a crank chamber is fed into a valve chamber having an exhaust valve and an intake valve, and a cam chamber accommodating a cam for driving the exhaust and intake valves.
However, when the engine unit is driven in an inclined or inverted posture, the condition of the oil mist is changed, so that it is difficult to control the lubricating of the engine unit.